The present invention relates to a packet configuring method and a packet receiver. Particularly, the present invention relates to a packet configuring method and a packet receiver, each for configuring a packet that contains training sequences in an asynchronous packet communication mode.
FIG. 7 is a diagram illustrating a down-link control channel frame used for the conventional digital automobile telephone, described ETSI/GSM, “Recommendation GSM 05.02 Multiplexing and Multiple Access on the Radio Path”, version 3.3.0, 15, Apr., 1989. FIG. 7 shows an example of a 10-channel configuration being the head of a frame. This frame is formed of a frequency connection channel (FCCH) 1000, a synchronization channel (SCH) 1001 and a broadcast channel (BCCH) 1002. The slot forming SCH 1001 or BCCH 1002 is formed of the training portion 1011 and the data portions 1010 sandwiched by the training portion 1011. The frequency connection channel FCCH 1000 is formed of a sine wave signal with a single frequency.
The mobile station that receives the control channel operates as follows: First, the mobile station receives FCCH 1000 and then corrects a variation in frequency (frequency offset) between a transmitter and a receiver. Then, the mobile station demodulates the synchronization channel SCH 1001 and the broadcast channel BCCH 1002.
SCH 1001 and BCCH 1002 are demodulated as follows: First, a channel impulse response is obtained using the training portion 1011. SCH 1001 and BCCH 1002 are demodulated by setting the reception parameter for the receiver based on the resultant channel impulse response. That is, the training portion 1011 is used for the initializing of the receiver.
According to the conventional art described above, frequency offset compensation and channel impulse response estimation necessary for signal reception are differently obtained.
In the automobile telephone system where communications are not always established through a base station but either communications via the base station or direct communications between terminals are established, for example, in local area networks (LANs), there is the possibility that different signal transmission sources are used for respective packets. This requires the receiver to execute frequency offset compensation and channel impulse response estimation every packet reception. In such a case, it may be considered, as shown in FIG. 8, that both the sequences 1020 for frequency offset estimation and the sequences 1021 for channel impulse response estimation are contained in the training sequences.
There is the method where the receiver monitors, for example, the reception power and the packet transmission to detect a transmitted packet in an asynchronous packet transmission and detects when the reception power exceeds a predetermined threshold value. In this case, the head of a packet cannot be already received accurately due to influences of noises or radio transmission path. Hence, this method has the disadvantage in that the boundary between the sequence for frequency offset estimation and the sequence for channel impulse response estimation may not be recognized.
Moreover, the method has the disadvantage in that the length of a training sequence is prolonged using the sequence for frequency offset estimation and the sequence for channel impulse response estimation, whereby the transmission efficiency is degraded.